Thermally developable diazotype copying materials

ABSTRACT

A thermally developable diazotype copying material is manufactured which comprises a supporting sheet and a lightsensitive copying layer coated on said supporting sheet, said layer consisting of a water soluble light-sensitive diazo compound, a water soluble heat fugitive acidic salt (base generating agent) and a water insoluble coupler. Another thermally developable diazotype copying material is also obtained, which is of a similar structure but said copying layer further contains an additional component consisting of an agent for lowering the melting point of said coupler besides said diazo compound, said salt and said coupler.

O United States Patent 1151 3,642,483 Kubo et a1. Feb. 15, 1972 [54]THERMALLY DEVELOPABLE 3,326,686 6/1967 Randall et a1. ..96/49 XDIAZOTYPE COPYING MATERIALS 3,360,369 11/1967 Amariti eta1.. ..96/753,389,995 6/ 1968 Tripp et al. ..96/49 X [72] Inventors: Keishi Kubo,Tokyo; Sadao Matsumura,

[73] Assignee: v Kabushiki Kaisha Ricoh, Tokyo, Japan 1,045,714 10/1966Great Britain ..96/49 907,724 10/1962 Great Britain ...96l49 1 09L 1967642,613 5/1964 Belgium ...96/75 21 A LN J 7 1 3 1,041,022 9/1966 GreatBritain. ...96/75 1 pp 0 1,376,709 9/1964 ,France ...96/75 6,404,16410/1964 Netherlands... ...96/75 [30] Foreign Application Priority Data800,956 12/1968 Canada ..96/91 Nov. 7, 1966 Japan ..41/72900 Nov. 18,1966 Japan ..41/75823 OTHER PUBLICATIONS D' .,R ,F .196, s2] u.s.c|..96/75,96/49,96/91 1 ,i i i 5 epmducm Rev'ew eb 2 pp [51] lnt.ClG03cl/60,G03c1/54,G03c1/58 & E n v 1 5 4 1961 58] Field 61 Search..96/49, 75,91; 117/367, 36.8; 2 32;"

Primary Examiner-Charles L. Bowers, Jr. [561 Reierems Attorney-Woodhams,Blanchard and Flynn UNITED STATES PATENTS 57] ABSTRACT gfi j i 42 Athermally developable diazotype copying material is manu- 3064049 11,1962 C m e a [91 x factured which comprises a supporting sheet and alight-sensi- 5398 1 196 96 75 x tive copying layer coated on saidsupporting sheet, said layer 4 1 I a1 4 91 consisting of a water solublelight-sensitive diazo compound,a 5991 6/ l 0 euge ouer et I watersoluble heat fugitive acidic salt (base generating agent) 2239'7044/1941 de et "96/9l x and a water insoluble coupler. Another thermallydevelopable 3,199,982 8,1965 Kash'wabara'm diazotype copying material isalso obtained, which is of a 3,202,510 8/1965 Hollmann ..96/91 SimilarStructure but Said copying layer further contains an 33551007 6/1966K053: "96/91 X ditional component consisting of an agent for loweringthe 3,255,011 6/1966 Welch .....96/91 X melting point of said couplerbesides said diazo compound, 3,271,155 9/1966 Aebi .96/91 X said saltand said coupler. 3,301,679 1/1967 Halperin et al. ..96/91 X 2 Claims,No Drawings THERMALLY DEVELOPABLE DIAZOTYPE COPYING MATERIALS BACKGROUNDOF THE INVENTION 1. Field of the Invention The present invention isconcerned with thermally developable diazotype copying materials havingfeatures which are represented particularly by the markedly improvedcolor developing ability and shelf life, which are manufactured byforming, on the supporting sheet, a light-sensitive layer containing alight-sensitive diazo compound, a base generating agent consisting of awater soluble heat fugitive acidic salt and a coupler, or by theprovision of a light-sensitive layer containing said respectivecomponents and additional agent for lowering the melting point of saidcoupler.

2. Description of the Prior Art Among the conventional, thermallydevelopable diazotype copying materials, it is known to use those havingthe structure which comprises (1) a support sheet carrying thereon alight-sensitive copying layer containing a water soluble lightsensitivediazo compound, a water soluble coupler and a base generating agentconsisting of a nitrogen-bearing compound, and those having thestructure wherein (2) a mixture of a water insoluble or hardly solublelight-sensitive diazo compound, a coupler having an insoluble or hardlysoluble nature and an alkaline component all of which are in the form offine particles and constitute a light-sensitive layer dispersed in abinder which is adapted to unite the light-sensitive layer to thesupporting sheet. However, the first-mentioned copying materials had theshortcoming that, during storage, the base generating agent becamedispersed and was transferred into the supporting sheet even at normaltemperature, resulting in a reduction in the developing ability (orcolor developing ability). Accordingly, when prior art copying materialswhich had undergone such degenerating changes of the copying layers wereexposed to actinic light under originals and were then subjected to heatdevelopment, the result of their development was often found to be poorin quality so that it was impossible to obtain prints having asatisfactory image density. This shortcoming of the prior art copyingmaterials was compensated for either by increasing the base generatingagent content of the light-sensitive layer or by conducting thedevelopment at a temperature slightly higher than the proper developmenttemperature for these copying materials. However, the inclusion of thebase generating agent in the lightsensitive layer to an extent more thanthe necessary amount led to the formation of a large amount of productsresulting from thermal decomposition, during the process of heatdevelopment, hampering the proper development of the transferred image.Not only that, but also such an inclusion of an excess amount of a basegenerating agent caused these heat decomposition products to adhere tothe face of the portions of the sheet carrying the printed image, whichstained the print. Furthermore, when the development was conducted atsuch an elevated temperature, a part of the light-sensitive diazocompound tended to decompose and, as a result, the print did not have asatisfactory image density. The secondmentioned prior art copyingmaterials carrying a light-sensitive layer consisting of fine particlecomponents had the shortcoming that the coupling velocity (or the colordeveloping velocity) of the light-sensitive diazo compound and thecoupler contained in the light-sensitive layer was somewhat smaller thanthat of said first-mentioned copying materials having theirlight-sensitive layers made with a water-soluble light-sensitivecomponent, and involved a difficulty in forming a clear image on theprint.

SUMMARY OF THE INVENTION It is, therefore, the primary object of thepresent invention to eliminate the aforesaid shortcomings of the priorart and to provide thermally developable diazotype copying materialshaving superior copying ability, by forming a light-sensitive layer withthe principal components consisting of a combination of a water solublelight-sensitive diazo compound, a water insoluble coupler with orwithout an agent for lowering the melting point of said coupler, and abase generating agent consisting of a water soluble heat fugitive acidicsalt.

Another object of the present invention is to provide thermallydevelopable diazotype copying materials which permit the colordevelopment at an increased velocity during the development process andwhich permit the formation of clear images on the prints and which areof a markedly improved shelf life.

The water soluble light-sensitive diazo compounds which are used in thepresent invention are double salts of zinc chlorides or cadmiumchlorides and the compounds which include, for example:

P-dimethyl-aminobenzene-diazonium chloride,

P-diethyl-aminobenzene-diazonium chloride,

P-methyl-hydroxyethyl-aminobenzene-diazonium chloride,

and P-ethyl-hydroxyethyl-aminobenzene-diazonium chloride. The waterinsoluble couplers which are used in the present invention include, forexample, 2,3-dihydroxy-naphthalene,2,3-dihydroxy-6-sulfonamide-naphthalene, 2,3-dihydroxy-6- dihydroxyethylsulfonamide-naphthalene, l-carboxy-2,3- dihydroxy-naphthalene, 1,4-dichloro-2 ,3-dihydroxynaphthalene, and3,3'-dihydroxy-Z-naphthanilide. These water insoluble couplers are usedin the form of fine particles or powder.

The water soluble heat fugitive acidic salts include, for example, suchwater soluble salts which are the compounds formed with the substancesof the following two groups: (1) water soluble heat fugitive acids whichare represented, for example, by halogenoacetic acids such asmonochloroacetic acid, dichloroacetic acid and trichloroacetic acid;derivatives of acetic acid, such as cyanoacetic acid and halogenomalonicacid such as dichloromalonic acid, and (2) alkali metals such as sodiumand potassium, or basic components such as ammonia, ethanolamine andisopropylamine. According to the present invention, these salts areadded to said diazo compound in an amount preferably ranging from 4parts by weight to 7 parts by weight per part by weight of such a diazocompound.

The agents for lowering the melting points of the couplers, which areused in the present invention, include guanidine-tartaric acid salt(having a melting point of 164 C.) and the derivatives of guanidinewhich include, for example:

Aminoguanidine-hydrochloric acid salt (melting point being 163 C.),

Cyanoguanidine (melting point being 208 C.),

Ethylbiguanide-hydrochloric acid salt (melting point beingDimethylbiguanide-hydrochloric acid salt (melting point being 216 C.),

3-methoxy benzoguanidine (melting point being 204 C.

l-butyl-B-nitroguanidine (melting point being 84 C. and

2-guanyl phthalic acid amide (melting point being 166 C.

Said agents further include acid amides such as acetamide (melting pointbeing 82 C.), acrylamide (melting point being 85 C.), propionamide(melting point being 79 C.), butylamide (melting point being 116 C.) andmalonamide (melting point being C.). The aforesaid agents for loweringthe melting points of the couplers are invariable water soluble.

The present invention is concerned, therefore, with copying materialswhich are formed by providing, on a supporting sheet such as paper,precoated paper and plastic foil, a lightsensitive layer which consistsof an appropriate combination of the aforesaid respective componentsconstituting a lightsensitive layer.

Next, description will be directed to one example of the presentinvention to explain in detail the ability and the effect accruingtherefrom of the copying materials of the present invention. Said oneexample of the present invention is represented by a thermallydevelopable diazotype copying material having a structure wherein asupporting sheet carries thereon a light-sensitive layer containing thefollowing three components, i.e., one of the aforesaid diazo compounds,one of the aforesaid couplers and one of the aforesaid water solublesalts. This coping material is featured by an extremely increaseddevelopment velocity which is displayed when the exposed copyingmaterial is subjected to the development process, as compared withconventional copying materials. This difference can be explained by thefollowing facts. The conventional copying materials employing, as thebase generating agent in general, a nitrogen-bearing compound such asurea or the derivatives thereof present impaired color developingability at the time of heat development for the reasons that have beenstated previously, with the result that the obtained prints do not havea satisfactory color density. In contrast to this, the base generatingagent of the present invention employs a water soluble heat fugitiveacidic salt such as monochloroacetic acid, dichloracetic acid andtrichloroacetic acid, so that the color development velocity of thecopying material of the present invention containing such a basegenerating agent increases, and accordingly, a print bearing asatisfactory image density is obtained.

However, these heat fugitive acidic salts have a tendency to cause theoccurrence of a premature coupling phenomenon which is represented bythe coupling between the light-sensitive diazo compound and the couplerboth of which are contained in the light-sensitive layer, which takesplace at normal temperature, leading to the fog phenomenon which impairsthe shelflife of the copying materials. Therefore, when it is intendedto use a nitrogen-bearing compound as the base generating agent, it isnecessary to explore the color development agents to improve the colordevelopment ability which is to be displayed at the time heatdevelopment is conducted. Contrariwise, when it is intended to use heatfugitive acidic salts, it is necessary to use a color developmentsuppressing agent for preventing the occurrence of this fog phenomenon.As a means for suppressing the color development, it is considereduseful to form an intermediate layer consisting of a waxlike substancefor being interposed between the light-sensitive diazo compound and thecoupler. However, the formation of such an intermediate layer willimpair satisfactory coupling between the light-sensitive diazo compoundand the coupler at the time of the heat treatment, resulting in a markeddeterioration in the color development of the obtained image on theprint.

According to the present invention, however, the occurrence of theaforesaid premature coupling phenomenon is arrested by the particularuse ofthe water insoluble couplers. By virtue of the use of these waterinsoluble couplers, there hardly takes place a coupling between thelight-sensitive diazo compounds and the couplers at normal temperatureeven where the water soluble heat fugitive acidic salts have undergonedecomposition to some extent, so that, as a result, there occurs noimpairment of the color development in the image formed on the printobtained. Instead, the coupler gains its coupling activity for the firsttime from the heat development, and the coupler is allowed, by this heattreatment, to be united with the water soluble light-sensitive diazocompound to quickly form a dye image. The adoption of the waterinsoluble couplers in the present invention thus contributes to theprovision of thermally developable copying materials which are ofsuperior color developing ability and an improved shelf life.

According to the present invention, the copying materials may be made byfirst applying a coupler onto the supporting sheet and then applying amixture ofa diazo compound and a water soluble heat fugitive acidic saltto the resulting first layer to form a light-sensitive layer on thesupporting sheet. Or, alternatively, the light-sensitive layer may beformed by applying a mixture of the aforesaid three components onto thesupporting sheet. However, the former copying material of the presentinvention which carries a light-sensitive layer consisting of theaforesaid two layers, i.e., a first layer of coupler and a second layerconsisting of said mixture is somewhat superior in shelf life to thelatter copying material which is a single layer type. In each of thesetwo types of copying materials, however, the water insoluble coupler isprovided in the form of a solution such that the coupler is dispersed ina vinyl acetate emulsion.

According to the present invention, the aforesaid series of agentsadapted for lowering the melting point of the couplers are provided asone of the components constituting the lightsensitive layer in order tofurther improve the color developing ability of the coping materialsduring the development process.

Now, the inclusion, in the light-sensitive layer, of a water solubleagent, such as guanidine, its derivatives and acid amides, adapted forlowering the melting point of the coupler jointly with the othercomponents constituting the light-sensitive layer, or the inclusion ofsuch an agent in the layer of the aforesaid water insoluble coupler,leads to a markedly lowered eutectic point of the water insolublecoupler by virtue of the multiplying action effected by the coupler andthe agent, with the result that the velocity of coupling (or the colordevelopment velocity) between the light-sensitive diazo compound and thecoupler at the time of heat development is further increased, leading toan improved color developing ability as well as the materialization ofhigh density images on the prints obtained. This improved colordeveloping ability of copying materials permits a reduction in thecontacting time of the heated rollers. This reduced contacting time ofthe heated rollers, in turn, leads to the advantages that not only themanufacture of copying apparatuses is economized by the simplifieddeveloping mechanism which is incorporated in such apparatuses, but alsothe production of copying apparatuses of compact size becomes possible.

Next, some examples of the eutectic points resulting from the additionof the aforesaid compounds which give an eutectic effect to the waterinsoluble couplers are shown in the following t a ble.

As is clear also from the above table, it is desirous that the agent forlowering the melting point of the coupler be admixed to the coupler inanamount which is represented by the eutectic ratio by weight. Ordinarily,however, the agent is added in an amount ranging from 0.14 parts byweight to 0.25 parts by weight per part by weight of the coupler used.

As has been understood from the foregoing description, the presentinvention is concerned with thermally developable diazotype copyingmaterials which thoroughly satisfy various requirements, such as theinstantaneously effected coupling at a low temperature and the improvedshelf life, which are demanded of thermally developable diazotypecopying materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 To said solution (A)containing a light-sensitive diazo compound was added said solution (B)prepared by dispersing a water-insoluble coupler in a vinyl acetateemulsion. The lightsensitive solution which was obtained from thoroughlydispersing (B) in (A) was applied to a supporting sheet and was dried.As a result, a thermally developable diazotype copying material wasobtained.

An original was placed on the copying material thus obtained and theresulting assembly was exposed to actinic light by irradiatingultraviolet rays thereto. Thereafter, the exposed sheet was subjected toheat development by passing it over a roller heated to a temperatureranging from 140 to 160 C. for 2 to 3 seconds, and a print bearing aclear blue image was obtained.

A comparison of shelf life between the copying material of the presentinvention and a conventional copying material (whose light-sensitivelayer contains a water soluble coupler and2,3-dihydroxy-naphthalene-fi-sodium sulphate) was conducted bysubjecting these two copying materials to coercive ageing by preservingthem under the conditions consisting of a temperature which was 50 C.and a relative humidity which was 20 percent. More specifically, thesetwo copying materials which have undergone coercive ageing for apredetermined period of time were exposed and developed in a manner asdescribed above. It was confirmed that the copying material of thepresent invention showed an improved shelf life which was two to threetimes longer than that of the conventional copying material.

EXAMPLE 2 Solution (A):

Water 80 cc. P-dimethyl-aminobenzene diazonium chloride-zinc chloridedouble salt l.0 g. Trietha nolamine trichloroacetate 6.0 g. Tartaricacid 0.6 g. Solution (B):

Water 20 cc. 2,3-dihydroxy-6-sulfonamide-naphthalene 3.0 g.

Vinyl acetate emulsion (content: 50%) 4.0 g.

The light-sensitive solution (A) containing a light-sensitive diazocompound was admixed with the solution (B) prepared by dispersing awater insoluble coupler in a vinyl acetate emulsion which was thenthoroughly dispersed in said solution (A). The resulting light-sensitivesolution was applied to a supporting sheet and was dried, and thus, athermally developable diazotype copying material was obtained.

An original was placed on the face of the light-sensitive layer of thecopying material thus obtained and they were exposed to actinic lightwhich was done by the application of ultraviolet rays thereto, and thiswas followed by heat development conducted by passing the exposed sheetover a roller heated to a temperature ranging from 140 to 160 C. for 2to 3 seconds. As a result, a print bearing a very clear blue image wasobtained.

This copying material showed a shelf life which was in the order similarto that of the copying material of the present invention obtained inExample 1.

EXAMPLE 3 Water I00 cc. 2.3-dihydroxy-fi-sulfonamide-naphthalene 3.5 3.Vinyl acetate emulsion (content: 50%) 4.0 3. Fine powder of silica(grain size: l-5 microns) 2.0 g.

The above solution was applied to the face of a supporting sheet and wasdried to form a coupler-bearing layer. Thereafter, a light-sensitivesolution containing a light-sensitive diazo compound consisting of:

Water cc P-ethyl-hydroxyethyl-aminobenzene diazonium chloride-zincchloride double salt l.0 g. Sodium trichloroacerate 6.0 g. Tartaric acid0.5 g .Saponin 0.l g

was applied to the upper face of the aforesaid coupler-bearing layer andwas dried. Thus, a thermally developable diazotype copying material wasobtained.

An original was placed on the light-sensitive layer of the copyingmaterial thus obtained. The assembly was exposed to actinic light whichwas done by applying ultraviolet rays thereto. Thereafter, the exposedsheet was subjected to heat development by passing it over a rollerheated to -160 C. for 2 to 3 seconds. As a result, a print bearing avery clear blue image was obtained. This copying material was found tobe of an improved shelf life which was nearly 20 percent superior tothose of the copying materials obtained in Examples 1 and 2.

EXAMPLE 4 Solution (A):

Water 80 cc. P-ethyl-hydroxy-ethyl-aminobenzene diazonium chloridezincchloride double salt l.0 g. Sodium trichloroacetate 6.0 g. Tartaric acid0.6 g. Cyanoguanidine 0.5 g. Saponin 0.1 g. Solution (B):

2,3-dihydroxy-naphthalene 2.0 g. Vinyl acetate emulsion (content: 50%)4.0

To the above solution (A) was added the solution (B) and the resultingsolution was thoroughly mixed. This mixture solution was then applied tothe upper face of a supporting sheet and was dried, with a result that athermally developable diazotype copying material was obtained. Anoriginal was placed on the face of the light-sensitive layer of thecopying material, and ultraviolet rays were irradiated thereto toperform exposure. Thereafter, the exposed sheet was heatdeveloped bypassing it over a roller heated to 140-150 C. for 2 to 3 seconds, withthe result that a print bearing a very clear blue image was obtained.The color density of this blue image and the color density of the imageobtained according to the present invention in Example 1 were measuredby the use of a reflection densitometer. It was confirmed that the imagedensity of the present example was 15 to 20 percent superior to that ofthe latter. Furthermore, the shelf life of the product of this examplewas measured by means of a coercive ageing in a manner similar to thatdescribed in Example l. [t was noted that the inclusion of an agent forlowering the melting point of the coupler in the light-sensitive layergave rise to no adverse effect.

EXAMPLE 5 Solution (A):

Water 80 cc. P-diethyl-aminobenzene diazonium chloridezinc chloridedouble salt 1.0 g. Trichloroacetic acid diisopropylarnine 6.0 g.Tartaric acid 0.6 g. Dimethylbiguanide (hydrochloride) 0.4 g.

Saponin 0.l g. Solution (B):

Water 20 cc. 2,3-dihydroxy-6sulfonamide-naphthalene 3.0 g. Vinyl acetateemulsion (content: 50%) 4.0 g.

After adding the above solution (B) to the solution (A) and thoroughlymixing them together, the resulting mixed solution was applied onto theupper face of a supporting sheet and was dried, with the result that athermally developable diazotype copying material was obtained. Afterprocessing this copying sheet and heat developing the same in a mannersimilar to that described in Example 4, a print bearing a very clearblue image was obtained. The image density and the shelf life of thiscopying material were both noted to be in the same order to those of thecopying material obtained in Example 4,

EXAMPLE 6 Water 100 cc. 2,3-dihydtoxy-6-sulfonamide-naphthalene 3.5 g.Vinyl acetate cmulsion (content: 50%) 4.0 g. Fine particles nt'silicu(grain size: l-S microns) 2.0 g. Aminoguanidine (hydrochloride) 0.5 g.

The above solution was applied onto a supporting sheet and was dried toform a layer containing a coupler. Thereafter, the upper face of thiscoupler-bearing layer was coated with a light-sensitive solutionconsisting of the following components:

Water 100 cc. P-methyl-hydroxyethyl-aminobenzene diazonium chloride zincchloride double salt 1.0 g. Sodium trichloroacetate 6.0 g. Tartaric acid0.5 g. Saponin O.l g.

and was dried, with the result that a thermally developable diazotypecopying material was obtained. An original was placed on the upper faceof the light-sensitive layer of this copying material. Exposure wasconducted by irradiating ultraviolet rays onto the assembly. Then heatdevelopment was conducted by passing the exposed sheet over a rollerheated to l40-l50 C. for 2 to 3 seconds. As the result, a print bearinga very clear blue image was obtained. It was confirmed that this copyingmaterial had an image density and a shelf life which were improved bynearly 20 percent over those of the copying materials obtained inExamples 4 and 5.

What is claimed is:

l. A thermally developable diazotype copying material having on onesurface of a supporting member a light-sensitive layer comprising abinder resin having dispersed therein a diazonium compound, an azocoupling compound, a base generating agent, an acidic stabilizer and acompound for lowering the melting point of said azo compound, in whicha. said diazonium compound is a water-soluble, light-sensitive,diazonium compound selected from the group consisting of zinc chlorideand cadmium chloride double salts of p-dimethyl-aminobenzene diazoniumchloride, pdiethyl-aminobenzene diazonium chloride,p-methylhydroxyethyl-aminobenzene diazonium chloride andpethylhydroxyethyl-aminobenzene diazonium chloride;

b. said base generating agent is a water-soluble, heat-fugitive, acidicsalt selected from the group consisting of a1- kali metal salts,ammonium salts, ethanolamine salts and isopropylamine salts ofhalogenoacetic acids, cyanoacetic acid and halogenomalonic acids;

c. said azo coupling compound is a water-insoluble azo coupling compounduniformly dispersed in said layer in the form of fine particles, saidcompound being selected from the group consisting of2,3-dihydroxy-naphthalene, 2,3-dihydroxy-fi-sulfonamide-naphthalene,2,3-dihydroxy-G-dihydroxyethyl sulfonamide-naphthalene, l-carboxy-2,3-dihydroxy naphthalene, l,4-dichloro-2,3-dihydroxy naphthalene and3,3-dihydroxy-Z-naphthanilide; and

(1. said compound for lowering the melting point of said azo couplingcompound is a water-soluble compound selected from the group consistingof guanidine-tartaric acid salt, aminoguanidine-hydrochloric acid salt,cyanoguanidine, ethylbiguanide-hydrochloric acid salt,dimethylbiguanide-h drochloric acid salt, 3-methoxy benzoguanldtne,-butyl-3-nitroguanrdine, Z-guanyl phthalic acid amide, acetamide,acrylamide, propionamide, butylamide and malonamide, the amount of saidcompound for lowering the melting point being in the range of 0.14 to0.25 part by weight per one part by weight of said azo coupling compoundand forming a eutectic with the azo coupling compound.

2. A thermally developable diazotype copying material having on onesurface of a supporting sheet a two-layer light-sensitive coatingcomprising a diazonium compound, an azo coupling compound, a basegenerating agent, an acidic stabilizer and a compound for lowering themelting point of said azo coupling compound, in which a. the first layerconsists of a binder resin containing a water-insoluble azo couplingcompound uniformly dispersed in said binder resin in the form of fineparticles and a compound for lowering the melting point of said azocoupling compound, said azo coupling compound being selected from thegroup consisting of 2,3-dihydroxy-naphthalene,2,3-dihydroxy-naphthalene-6-sulfonamide-naphthalene,2,3-dihydroxy-6-dihydroxyethyl-sulfonamide-naphthalene,l-carboxy-2,3-dihydroxynaphthalene,l,4-dichloro-2,3-dihydroxy-naphthalene and3,3'-dihydroxy-2-naphthanilide; and said compound for lowering themelting point of said azo coupling compound being selected from thegroup consisting of guanidine-tartaric acid salt,amino-guanidine-hydrochloric acid salt, cyanoguanidine,ethylbiguanide-hydrochloric acid salt, dimethyl-biguanide-hydrochloricacid salt, 3- methoxy benzoguanidine, l-butyl-3-nitroguanidine, 2-guanyl phthalic acid amide, acetamide, acrylamide, propionamide,butylamide and malonamide, the amount of said compound for lowering themelting point being in the range of 0.14 to 0.25 part by weight per onepart by weight of said azo coupling compound and forming a eutectic withthe azo coupling compound;

b. a second layer containing a water-soluble, light-sensitive diazoniumcompound, a water-soluble, heat-fugitive, acidic salt as the basegenerating agent and an acidic stabilizer, said second layer overlyingsaid first layer, said diazonium compound being selected from the groupconsisting of zinc chloride and cadmium chloride double salts ofp-dimethyl-aminobenzene diazonium chloride, pdiethyl-aminobenzenediazonium chloride, p-methylhydroxyethyl-aminobenzene diazonium chlorideand pethylhydroxyethyl-aminobenzene diazonium chloride, and saidheat-fugitive acidic salt being selected from the group consisting ofalkali metal salts, ammonium salts, ethanolamine salts andisopropylamine salts of halogenoacetic acids, cyanoacetic acid andhalogenomalonic acids.

2. A thermally developable diazotype copying material having on onesurface of a supporting sheet a two-layer light-sensitive coatingcomprising a diazonium compound, an azo coupling compound, a basegenerating agent, an acidic stabilizer and a compound for lowering themelting point of said azo coupling compound, in which a. the first layerconsists of a binder resin containing a water-insoluble azo couplingcompound uniformly dispersed in said binder resin in the form of fineparticles and a compound for lowering the melting point of said azocoupling compound, said azo coupling compound being selected from thegroup consisting of 2,3-dihydroxy-naphthalene,2,3-dihydroxy-naphthalene-6-sulfonamide-naphthalene,2,3-dihydroxy-6-dihydroxyethyl-sulfonamide-naphthalene,1-carboxy-2,3-dihydroxy-naphthalene,1,4-dichloro-2,3-dihydroxy-naphthalene and3,3-dihydroxy-2-naphthanilide; and said compound for lowering themelting point of said azo coupling compound being selected from thegroup consisting of guanidine-tartaric acid salt,amino-guanidine-hydrochloric acid salt, cyanoguanidine,ethylbiguanide-hydrochloric acid salt, dimethyl-biguanide-hydrochloricacid salt, 3-methoxy benzoguanidine, 1-butyl-3-nitroguanidine, 2-guanylphthalic acid amide, acetamide, acrylamide, propionamide, butylamide andmalonamide, the amount of said compound for lowering the melting pointbeing in the range of 0.14 to 0.25 part by weight per one part by weightof said azo coupling compound and forming a eutectic with the azocoupling compound; b. a second layer containing a water-soluble,light-sensitive diazonium compound, a water-soluble, heat-fugitive,acidic salt as the base generating agent and an acidic stabilizer, saidsecond layer overlying said first layer, said diazonium compound beingselected from the group consisting of zinc chloride and cadmium chloridedouble salts of p-dimethyl-aminobEnzene diazonium chloride,p-diethyl-aminobenzene diazonium chloride,p-methyl-hydroxyethyl-aminobenzene diazonium chloride andp-ethylhydroxyethyl-aminobenzene diazonium chloride, and saidheat-fugitive acidic salt being selected from the group consisting ofalkali metal salts, ammonium salts, ethanolamine salts andisopropylamine salts of halogenoacetic acids, cyanoacetic acid andhalogenomalonic acids.